This invention relates to high speed tape recorders and in particular, to a new and improved bias system for tape duplicating equipment.
In a tape duplicating operation, a master tape will be driven past a plurality of read heads and the signals from the reproduce heads will be transmitted to the corresponding record heads of each of a plurality of slave recorders operated in parallel. The entire system will operate at high speeds, typically 240 inches per second. The high speed operation and the utilization of a large number of slave recorders in parallel is essential for economic production of magnetic tape cartridges and cassettes. Control of various parameters of the master reproducer and the slave recorders, including electrical, magnetic and mechanical characteristics, is highly desirable.
In the recording operation, a high frequency bias signal is combined with the audio frequency information signal at each record head. It is highly desirable that the frequency of this bias signal be maintained constant and that the amplitude of the high frequency bias signal be maintained constant and also be adjustable, since different bias levels are preferred for different tapes and recording conditions, as well as for individual record heads. In the past, bias level has been provided by use of stable amplifiers, but these have not always been satisfactory, particularly with changes in temperature and passage of time. Also, when the bias level is set for each individual slave recorder and each individual head thereof, changes in bias level desired for changes in tape and/or recording conditions requires individual adjustment of each record circuit.
Accordingly, it is an object of the present invention to provide a new and improved central bias level control system for a plurality of slave recorders in high speed tape duplicating equipment. A further object is to provide such a system wherein the high frequency bias signal amplitude is controlled by high gain feedback circuits. An additional object is to provide such a system wherein the frequency of all bias signals can be controlled by a single oscillator at the master reproducer and whereby the amplitude of all bias signals can be adjusted by a single control at the master reproducer. One further object is to provide such a system wherein the bias amplitude at each individual record head can be individually adjusted, in addition to the overall control provided by the master reproducer.
It is an object of the invention to provide both apparatus and method for accomplishing these purposes. Other objects, advantages, features and results will more fully appear in the course of the following description.